Effects of Na4EDTA and EDTA on seeded precipitation of sodium aluminate solution

Micelle formation over a critical micelle concentration (CMC) is related to the economic removal of organics in a sodium aluminate solution. In this research, removal of organics was investigated by adding activated alumina and red mud. The micelle formation of sodium benzoate and sodium stearate, together with enthalpy, Gibbs free energy and entropy, was discussed by detecting the surface tension. The removal rate of organics was > 21% with activated alumina or red mud in a concentrated sodium aluminate solution. Increasing benzoate (or stearate) concentration and elevating temperature decreased the surface tension. Furthermore, the concentrated sodium aluminate solution remarkably increased the cross-sectional headgroup area of sodium stearate compared with that of sodium benzoate and led to a strong depletion interaction and small organic assembly on the surface. The low CMC, large cross-sectional headgroup area and strong depletion interaction of micelles on the surface reduced the removal rate of organics in the sodium aluminate solution compared with that in water.

Effects of CMC and Micelle Formation on the Removal of Sodium Benzoate or Sodium Stearate in a Sodium Aluminate Solution

The aluminum hydroxide precipitation process from sodium aluminate solution was studied by adding the new synthesized active seeds and industrial seed separately. The results show that the precipitation rate reached 47, 81, and 68% at 60 h by adding industrial seed, seed A, and seed B (active seeds), respectively. Specific surface area, composition, morphology, and particle size distribution of seeds/precipitated products from supersaturated sodium aluminate solutions were investigated by Brunauer, Emmett, and Teller (BET) analysis, X-ray crystallography (XRD) analysis, Scanning electron microscope (SEM) images, and Power-spectral-density (PSD) analysis. Also, to study and understand the functional groups on the surface of seed/precipitated products and precipitation mechanisms, Fourier-transform infrared spectroscopy (FTIR) analysis was recorded. The result showed that the precipitation rate of the active seeds is higher than that of the industrial seed owing to the higher surface area, more active sites, crystal defects, and finer particle size that cause rise to nucleation for gibbsite. Also, improved precipitation of aluminum hydroxide from sodium aluminate solution may be due to the predominant phase crystallized of bayerite in the composition of active seeds. The FTIR analysis shows that the decline of the precipitation process in the presence of industrial seed may be due to oxalate–Al bonds and the impurity of carbonate.

Influences of New Synthesized Active Seeds and Industrial Seed on the Aluminum Hydroxide Precipitation from Sodium Aluminate Solution

Combined effect of amino and carboxyl group in α-alanine on seeded precipitation of sodium aluminate solution

The physicochemical properties of sodium aluminate solutions are modified by adding different surfactants, and the variations of the surface tension, viscosity as well as the conductivity are investigated in detail. The modification of the properties of the solution is correlated with the aluminium hydroxide precipitation process from the solution (Bayer process). The results indicate that the precipitation ratio, the crystal size, as well as the intensity of the Al(OH)3 products can be enhanced after addition of certain types of surfactants. The chemical compositions of the surfactants are reported and it can be shown that novel types of surfactants prepared by mixing different, relatively cheaper components exhibit the potential to replace the more expensive recipes commercially available. These improvements to the precipitation process are interpreted as being due to modification of the properties of the sodium aluminate solution after addition of the surfactants.

Influences of novel surfactants on the physicochemical properties of sodium aluminate solution relevant to the aluminium hydroxide precipitation process

Shiwen Bi

Papers

Influences of novel surfactants on the physicochemical properties of sodium aluminate solution relevant to the aluminium hydroxide precipitation process